Slimes

We
believe that slimes were one of the earliest communal life forms
to appear on Shalimar. Slimes are simple sheets of cells which
stay attached to each other, in part by clinging to a foundation,
such as a stone in the water. Each cell functions independently:
there is no division of labor. The group probably derives some
evolutionary advantage from clinging to the stones, perhaps by
maintaining a favorable distance from the surface of the water.
The cells
form a very thin layer, because each one must receive some light.
This means that their sheet of cells is fragile, and so tends
to be found in sheltered, shallow water where the bottom is stony
or sandy. In a muddy environment, slimes could too easily be buried.
In rough water, the tissue of slimes is torn apart, and small
pieces or individual cells are carried away in the water, perhaps
to start new colonies elsewhere.

Slimes have chlorophyll, and may be green,
orange, brown, or purple. Small colonies tend to be clones of
a single cell, and so will all be the same color. Many different
colonies may take hold on larger expanses of rock and so may show
many colors.

Slimes reproduce by division. Their cells
divide into two completely, but the outer walls stay attached
to each other. Slimes also produce small, toughly shelled capsules
that contain their genetic material. These little packets are
carried all over the planet in the ocean, and can remain dormant
for long periods of time. This adaptation makes it possible for
slimes to survive unpredictable meteor conditions produced by
meteor strikes.

Some
of the slimes have developed into a thicker form which we have
called carpets. In these sheets some of the cells are stacked
on each other, forming little bumps. They look and feel different
from the very smooth sheets of the slimes. Stacking individual
cells allows the topmost ones to get closer to the light, and
raises them above any drifting silt. It does, however, reduce
the light that the lower cells receive.

As
the little towers get taller, they are more affected by the pressure
of currents in the water. Pieces of the carpet may be torn away,
especially if the lowest cells, which provide attachment, are
deprived of light. The towers are very close together, creating
small tubes between the cells in which nutrients can be transported.
The primary function of the lowest cells becomes to provide anchorage
to the base of the carpet of cells. Differentiation of function
begins as nutrients are transferred from cells higher up in the
tower.

We
believe that some of the towers continued to differentiate, with
the growing towers of cells closing around the channels that allowed
the topmost cells to feed the roots. Groups of towers grew taller,
fusing into stems, and branching a little at their tips to capture
more of the light energy available to them. Their bases grew to
provide more holding surface, creating a web of proto-roots.

Growing
stems made it possible for the towers to take hold at greater
depths. These plants continued to reproduce by division, and new
towers would start up from the roots. Having roots and stems also
made it possible for the towers to grow in sand, and, later, silt.
If they were being buried, they could simply keep growing and
get to the light again. They began to colonize shallow areas previously
not available to them.

Some
of the towers widened their topmost area into disks instead of
branches. We have called these plants buttons, as the simplest
ones look a bit like mushrooms. Flat disks tended to collect debris
unless the water was very clear, and so most forms have a downward
sloping topmost disk.

Another
innovation developed by these plants was branching. Stems began
to grow up to a certain height, and then to put forth some short
branches. Sometimes a central stem was grown where the plant branched,
and so the stem continued growing upward, with the branches in
tiers. Repeating the modules of the stem allowed the plants to
recover more quickly if a storm broke them. (The broken part could
also float away and take root elsewhere.) It allowed the plants to put
their light gathering cells close to the surface of the water.
Once the plants began to send up more than one shoot per branching
node, they were able to increase the lighted area that they filled.
These water plants grow prolifically on Shalimar in most places
where the water is warm and shallow.